abk

plinth area is a better parameter to compare builders but many more things do matter let me explain
the carpet area depends also on the thickness of the walls and the number of walls shared with other flats i.e a flat open on three sides will own all 9" walls wheras a flat which shares walls with other flat will have less wall space (9/2 = 4.5") hence will have more percentage of carpet area. But we generally like a flat to be open on 3 sides.

the construction of wall with bricks will have 9" or 10.5" with plastering as bricks are uneven whereas a wall built with blocks will be 6-7" thick.again a increase in carpet area for the same plinth area.
But blocks are not preferred by all, they have their own set of problems.
contd